What are the key principles of preventing Legionella?

Legionella spp. are strictly waterborne pathogens. Monitoring the hospital water system and prevention of aspiration of contaminated drinking water is the key principle of preventing Legionellosis.

What are the conclusions of clinical trials and meta-analyses regarding control of Legionella?

Hospital construction, choice of materials for water pipes and level of maintenance affect formation of biofilms and contamination with Legionella spp.

Monitoring of hospital water and risk assessment should guide the decision for point-of-use filters, physical (heating, ionization) or chemical (disinfection) prevention measures.

What are the consequences of ignoring the control of Legionella?

High levels of water contamination with Legionella spp. propagate severe nosocomial pneumonia in individual highly susceptible patients and are a risk for hospital wide outbreaks of Legionnaires´ disease.

Hospital-acquired outbreaks of legionellosis have been reported worldwide as have case series for specific i.e. immunocompromides patient populations. Clonal identity of water and clinical isolates was demonstrated in several reports.

Summary of current controversies.

The controversies concentrate on the timing, extent, technique and interpretation of environmental cultures and the best way to decontaminate hospital water systems.

i) Most European countries as well as the US Veterans Healthcare System recommend routine testing of hospital drinking water for the presence of Legionella spp. whereas the US CDC advises testing only after cases of legionellosis have been diagnosed. Routine testing is recommended, however, for transplant centers.

ii) The proportion of water sites colonized with Legionella might be a more valuable predictor for the risk of acquiring legionellosis than the concentration in individual samples.

iii) Technique of probing and microbiological workup of the samples has to follow accepted and standardized protocols to achieve comparable results.

iv) The minimal infectious dose of Legionella is not known, is most likely different in different groups of patients and depends from the predominant legionella species and serotypes. The basic question as to how many Legionella are necessary in the environment to cause infection in humans is still not answered!

v) Several modalities for the hospital water system as well as point of use measures are available.

What is the impact of Legionella and the need for control relative to infections at other sites or from other specific pathogens?

More than two thirds of legionellosis are community-acquired. Nosocomial cases are either part of an outbreak or have a high mortality risk in sporadic cases most likely in immunocompromised patients.

Overview of important clinical trials, meta-analyses, case control studies, case series, and individual case reports related to infection control and Legionella.

See Table I for a summary of relevant research.

Table I.

Summary of Current Legionella Research

Recommendation

Timing of Environmental Sampling

Action

WHO [2007]

Sampling according to individual risk assessment: Water Safety Plan

Define target and alert levels for risk populations

CDC [2003]All health care facilities

No recommendation for routine culturing

If ³ 1 case of nosocomial legionellosis

CDC [2003]Transplantation Units

Periodic culturing

Aim at undetectable levels of Legionellaspp. in the water systems of units caring for high risk patients

US Veterans Healthcare System [2008]

Routine culturing according to algorithm for annual evaluation

If ³ 30% of outletstested positive for L.pneumophila SG1

Most European Countries

Routine culturing of drinking water

High risk patients: Legionella spp. should not be detectableDifferent target levels for standard risk patients in individual countries

Controversies in detail.

See Table II for a summary of the controversies related to Legionella.

Table II.

Controversies related to Legionella

Measures

Methods

Comments

References

Design, operation and maintenance of hospital water systems

Skilled technical staffChoice of pipe materials

WHORogers 1994

Temperature control

Continuous or intermittent heating of the hot-water system > 50°Ce.g. “superheat and flush”Heating at the point of use (local boilers for the cold water system)

NochemicalsStress onwater-system, not all parts of the system can be sufficiently heated, boilers have to be replaced regularly

Best 1984Marchesi 2011

UV - Light

No chemicalsMay be effective in restricted areas and as an additional method

Franzin 2002

Chemical Disinfection

Copper-silver ionization

Regarded by many authors as the most effective long-term disinfection method
Monitoring of ion concentrations and water ph is mandatory

Modol 2007Chen 2008Shih 2010

Chlorine dioxide

Conflicting experiences are reported
BiocideProviding an effective concentration in the water system is challenging

Safe, easy to use e.g. in emergency situationsExpensive if used for larger areas

Sheffer 2005

What national and international guidelines exist related to Legionella?

In most countries recommendations regarding Legionella spp. are part of legal regulations for the quality of drinking water. Thus apart from the WHO recommendations, the CDC and European guidelines (ECDC) readers might refer to the national regulations of their country of interest.

What other consensus group statements exist and what do key leaders advise?

Several excellent and comprehensive overviews concerning prevention and control of Legionella have been provided by Lin, Stout and Yu.

The European Working Group for Legionella Infections (EWGLI) offers several guidelines concerning all aspects of management of Legionella spp.